Fukushima Toshiaki, Yoshihara Hidehito, Furuta Haruka, Hakuno Fumihiko, Iemura Shun-Ichiro, Natsume Tohru, Nakatsu Yusuke, Kamata Hideaki, Asano Tomoichiro, Komada Masayuki, Takahashi Shin-Ichiro
Department of Medical Science, Graduate School of Medicine, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima City, Hiroshima, 734-8553, Japan; Cell Biology Unit, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8501, Japan.
Laboratory of Protein Metabolism, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, 156-8506, Japan.
Biochem Biophys Res Commun. 2017 Mar 11;484(3):522-528. doi: 10.1016/j.bbrc.2017.01.101. Epub 2017 Jan 23.
Insulin receptor substrates (IRSs) are phosphorylated by IGF-I receptor tyrosine kinase in a ligand-dependent manner. In turn, they bind to and activate effector proteins such as PI3K, leading to various cell responses including cell proliferation. We had reported that ubiquitin ligase Nedd4 induces mono-ubiquitination of IRS-2, thereby enhancing IRS-2 tyrosine phosphorylation, leading to increased IGF signaling and mitogenic activity. Here we show that ubiquitin-specific protease 15 (USP15) antagonizes the effect of Nedd4 on IRS-2. We identified USP15 as a protein that preferentially bound to IRS-2 when IRS-2 was conjugated with ubiquitin. In HEK293 cells, Nedd4 overexpression induced IRS-2 ubiquitination, which was decreased by USP15 co-expression while increased by USP15 knockdown. Nedd4 overexpression enhanced IGF-I-dependent IRS-2 tyrosine phosphorylation, and USP15 co-expression suppressed it. Conversely, USP15 knockdown increased IRS-2 tyrosine phosphorylation and downstream signaling in prostate cancer PC-3 cells. We concluded that USP15 attenuates IGF-I signaling by antagonizing Nedd4-induced IRS-2 ubiquitination.
胰岛素受体底物（IRSs）以配体依赖的方式被IGF-I受体酪氨酸激酶磷酸化。反过来，它们与诸如PI3K等效应蛋白结合并激活这些蛋白，从而导致包括细胞增殖在内的各种细胞反应。我们曾报道泛素连接酶Nedd4诱导IRS-2的单泛素化，从而增强IRS-2的酪氨酸磷酸化，导致IGF信号传导增加和促有丝分裂活性增强。在此我们表明，泛素特异性蛋白酶15（USP15）拮抗Nedd4对IRS-2的作用。我们鉴定出USP15是一种在IRS-2与泛素结合时优先与IRS-2结合的蛋白。在HEK293细胞中，Nedd4的过表达诱导IRS-2泛素化，USP15共表达可使其降低，而USP15敲低则使其增加。Nedd4过表达增强了IGF-I依赖的IRS-2酪氨酸磷酸化，而USP15共表达则抑制了这种磷酸化。相反，在前列腺癌PC-3细胞中，USP15敲低增加了IRS-2酪氨酸磷酸化和下游信号传导。我们得出结论，USP15通过拮抗Nedd4诱导的IRS-2泛素化来减弱IGF-I信号传导。
